Batteries

Unit - V

Chapter 8

Batteries

INTRODUCTION

In electrochemical cells, the chemical energy is converted into electrical energy. The cell potential is related to free energy change (∆G). In an electrochemical cell, the system does work by transferring electrical energy through an electric circuit. Thus AG for a reaction is a measure of the maximum useful work, that can be obtained from a chemical reaction.

ie., ∆G = maximum useful work

But we know that maximum useful work = nFE

When a cell operates, work is done on the surroundings (flow of electricity).

∆G = - nFE (or)  ∆G < 0

Decrease in free energy is indicated by (-)ve sign.

One of the main uses of the galvanic cells is the generation of portable electrical energy. These cells are known asbatteries.

1. Battery

A battery is an arrangement of several electrochemical cells connected in series, that can be used as a source of direct electric current.

A Cell: It contains only one anode and cathode.

A Battery: It contains several anodes and cathodes.

2. Requirements of a battery

A useful battery should fulfil the following requirements

1. It should be light and compact for easy transport.

2. It should have long life both when it is being used and when it is not used.

3. The voltage of the battery should not vary appreciably during its use.